The present invention relates to vulcanizable rubber mixes which may be vulcanized without the release of nitrosamines with a high crosslink density and a high proportion of short sulfur bridges.
It is known from the prior art to prepare rubber vulcanizates with a high degree of crosslinking by vulcanizing the corresponding rubbers in the presence of sulfur in combination with known vulcanization accelerators such as sulfenamides, thiurams or carbamates. A disadvantage of using such vulcanization systems, however, is that relatively large amounts of crosslinking chemicals are required to obtain a high crosslink density in the vulcanizates. Another disadvantage is that the proportion of long-chain sulfur bridges in the vulcanizate is relatively high, which means that the heat resistance of the vulcanizates is unsatisfactory. We refer in this connection, e.g., to M. R. Kreijsa, J. L. Koenig, xe2x80x9cThe Nature of Sulfur Vulcanizationxe2x80x9d in Elastomer Technology Handbook, ed, by N. P. Cheremisinoff, p. 475 ff, CRC Press Inc., Boca Raton 1993; A. D. Thorn, R. A. Robinson, xe2x80x9cCompound Designxe2x80x9d in Rubber Products Manufacturing Technology, ed., by A. K. Bhowmick, M. M. Hall, H. A. Benarey, p 1 ff, Marcel Dekker Inc., New York 1994, and A. K. Bhowmick, D. Mangaraj, xe2x80x9cVulcanization and Curing Techniquesxe2x80x9d in Rubber Products Manufacturing Technology, ed., by A. K. Bhowmick, M. M. Hall, H. A. Benarey, p. 315 ff, Marcel Dekker Inc., New York 1994.
An object of the present invention is to provide vulcanizable rubber mixes which produce vulcanizates which have a high crosslink density and a high proportion of short-chain sulfur bridges. Moreover, the aim of the present invention is to execute vulcanization with vulcanization chemicals which do not release nitrosamines and are therefore ecologically acceptable. Moreover, the aim of the present invention was to obtain a high crosslink density of the vulcanizates with the lowest possible molar additions of crosslinking chemicals.
The present invention provides, therefore, vulcanizable rubber mixes containing
a) rubbers,
b) O,O-bis-(alkyl)dithiophosphoric acid polysulfides corresponding to the formula 
wherein
x represents 2, 3, 4 or 5 and
R represents a C8-C12-alkyl or -cycloalkyl radical
and
c) primary and/or secondary amines corresponding to the formula 
wherein
Y represents hydrogen or a mercaptobenzothiazole radical,
R1 represents hydrogen, C1-C6-alkyl, C5 or C6-cycloalkyl or C7-C12-aralkyl and
R2 has the same meaning as R1,
with the proviso that R1 and R2 do not simultaneously represent hydrogen,
wherein the components b) and c) are present in a molar ratio of from (0.5 to 1.5):1 and in a total amount of from 1.0 to 10 parts by wt. per 100 parts by wt. of rubbers in the rubber mixes.